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Workshop => Engine and Bottom End => Topic started by: Bowtie316 on October 06, 2013, 11:48:17 AM
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So I'm checking over an ESR 330 +4 stoke motor that a builder had put together. I am trying to do everything I can now to make sure it will last. I am working on opening up the coolant passage over the exhaust, and I am going to drill the piston where it is dimpled at the 2 bridges by the main exhaust port. My question now has to do with ring end gap, I measured mine and the top ring is .014" and the bottom is .013". This is within factory spec of .010-.020" but I would think with bigger bore would come bigger ring end gap spec.
Is this safe to run as is or should I open it up?
Wiseco website says .004 x bore in inches for top ring and .005 x bore for second ring, which for my 76mm bore would be .012 and .015" respectively. I would thing that due to the top ring running hotter you would want a bit wider gap there. That's what we do on turbo engines.
Thanks for any help.
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I really did not know there was any difference. 2 rings come with the piston. I thought they were exactly the same. I understand the concept of making you own end gap by choice when ordering rings without any gap. Cut the gap so when it gets to operating temperature there is no gap and you get no blow by. I am sure the manufacturer has some safety margin built in when they ship the normal rings to us. Seems to be a little extreme IMO to check them and change them. I would think your piston to bore clearance and break in were more important to making the piston last.
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I allways check the buttgap on the rings.I thought the oem specs were 12 to 20. I would do as suggested by wiesco .I have helped at least 2 friends over the years that did not check there gap and had low compression after there first real heat cycle
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I do believe the rings are the same, probably just manufacturing tolerance that I am seeing. I know I'm being anal. I'm just afraid with it being as tight as it is, if the ring gap closes to zero or past, it can create lots of problems such as excessive heat, ring catching a port and ruining piston and cylinder, or busting the ring land out the top of the piston. I'll probably just open up the bottom ring a tiny bit so that it is a little bigger than the top ring and call it good.
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Also, can anyone tell me if this is the new style piston, the one that won't have port linking issues?
(http://[URL=http://s851.photobucket.com/user/bowtie316/media/20131006_115936_zps67633787.jpg.html][IMG]http://i851.photobucket.com/albums/ab73/bowtie316/20131006_115936_zps67633787.jpg)[/URL][/IMG]
(http://[URL=http://s851.photobucket.com/user/bowtie316/media/20131006_120000_zpsa34583b3.jpg.html][IMG]http://i851.photobucket.com/albums/ab73/bowtie316/20131006_120000_zpsa34583b3.jpg)[/URL][/IMG]
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what it does if there is to little gap is wear the rings in out of round .once they cool and are relaxed they don't seal to the round bore
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That is the piston bowtie. Sounds like wosner has copied it now as well.
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That is the piston bowtie. Sounds like wosner has copied it now as well.
Thanks etccb, that makes me feel better. I'm going out to try to check port timing (something I've never done before), then hopefully I can get it put back together.
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Ring end gap should be no less than .012" on that bore size. It is good practice for the second ring to have about .003-.005" more end gap than the top. The reason is to prevent pressure build up between the the rings at peak cylinder pressure. On four strokes we see this happen by observing oil being pushed out the crankcase vent. The pressure builds up between the 2 rings and can lift the top ring off the ring land causing a loss of compression or blow by.
There I have told you all an engine building secret!
If you use .004" ring end gap per inch of bore size you should be pretty save. Remember a thousandth of inch end gap is nothing compared to the circumference of the bore. Don't make your self crazy about ring end gap, just don't get it to tight.
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That is the piston bowtie. Sounds like wosner has copied it now as well.
Hummm, so your saying Wossnor has switched over to the new type machining on the sides as well ???. I guess things do change.
Got a pic for sure, cause I would like to see if it as same as ESRs.
Kinda crazy how it works out, begged till I was blue in the face to try & get Dave to change over the machining on the Wossnors, but when I talked to Eddie about it, as quick as Wiseco could change over for ESR it was a done product & now on the shelf.
Neil
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Hummm, so your saying Wossnor has switched over to the new type machining on the sides as well ???. I guess things do change.
Got a pic for sure, cause I would like to see if it as same as ESRs.
Kinda crazy how it works out, begged till I was blue in the face to try & get Dave to change over the machining on the Wossnors, but when I talked to Eddie about it, as quick as Wiseco could change over for ESR it was a done product & now on the shelf.
Neil
thanks neil for all your efforts.I know from old threads that you are the one who brought this to light
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Bowtie.
Before you slip the cylinder on, check those piston sir clips out real good. It might be just how the pic makes them look, but that one sure dont look like its deep enough in its groove.
Its not impossible, that something could have happened during machining & the clip groove not be deep enough in that piston, but just check them out.
Wrist pin clips can come out sometimes, just ask anyone that has used several Mercury outboard engine over the years.
Neil
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Also check your wrist pin for endplay between the installed circlips. Check your circlips so that they appear to be expanded to at least half their wire thickness below the wrist pin bore. Check to see if the expanded circlip is not below the pin bore surface. Spending an additional 30 seconds when installing a piston will allow one to catch shallow circlip grooves, improper circlip wire diameter and wrist pins that are too long for the space between the circlip grooves.
Wiseco had a batch of wrist pins a few years ago that were about .010" to .020 too long. The circlip would start to expand in it's groove but the end of the wrist pin touching the circlip would not allow the circlip to fully expand and seat in the circlip groove. The wrist pin would eventually push the circlip out of the pin bore. If you have a lathe with carbide tooling, it only takes a couple of minutes to machine the wrist pin to fix the problem. Customers doing their own top ends that did not pay attention to the above detail did not catch this problem and it destroyed their top ends.
A bevel on the ends of the wrist pin is also a design where the bevel exerts additional circlip expanding pressure to hold the circlip in a properly machined circlip groove. The circlip groove depth needs to be at just a little bit more than half the thickness of the circlip wire.
The circlip wire diameter needs to be large enough to prevent the circlip from relaxing at high RPMs as the piston approaches top and bottom dead center. Installing the circlip so that the opening of the circlip is facing up or down will also raise the RPM limit where the circlip experiences enough acceleration that it will relax and come out of the groove. We had a lot of problems with circlips coming out of the grooves on some of the highly modified Kawasaki Quads around 1986 or 1987. Kawasaki cured the problem by increasing the wire diameter of the circlip and machining the circlip grooves for the larger wire diameter.
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damn we got all the good guys on here
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isnt it common knowledge not to machine in front of the wristpin. wiseco did this same crap years ago with cr500 pistons. aparently they didnt learn anything
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damn we got all the good guys on here
No doubt about it Fred.
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No doubt about it Fred.
thanks for agreeing with me but Im really the highwayman
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Bowtie.
Before you slip the cylinder on, check those piston sir clips out real good. It might be just how the pic makes them look, but that one sure dont look like its deep enough in its groove.
Its not impossible, that something could have happened during machining & the clip groove not be deep enough in that piston, but just check them out.
Wrist pin clips can come out sometimes, just ask anyone that has used several Mercury outboard engine over the years.
Neil
Also check your wrist pin for endplay between the installed circlips. Check your circlips so that they appear to be expanded to at least half their wire thickness below the wrist pin bore. Check to see if the expanded circlip is not below the pin bore surface. Spending an additional 30 seconds when installing a piston will allow one to catch shallow circlip grooves, improper circlip wire diameter and wrist pins that are too long for the space between the circlip grooves.
Wiseco had a batch of wrist pins a few years ago that were about .010" to .020 too long. The circlip would start to expand in it's groove but the end of the wrist pin touching the circlip would not allow the circlip to fully expand and seat in the circlip groove. The wrist pin would eventually push the circlip out of the pin bore. If you have a lathe with carbide tooling, it only takes a couple of minutes to machine the wrist pin to fix the problem. Customers doing their own top ends that did not pay attention to the above detail did not catch this problem and it destroyed their top ends.
A bevel on the ends of the wrist pin is also a design where the bevel exerts additional circlip expanding pressure to hold the circlip in a properly machined circlip groove. The circlip groove depth needs to be at just a little bit more than half the thickness of the circlip wire.
The circlip wire diameter needs to be large enough to prevent the circlip from relaxing at high RPMs as the piston approaches top and bottom dead center. Installing the circlip so that the opening of the circlip is facing up or down will also raise the RPM limit where the circlip experiences enough acceleration that it will relax and come out of the groove. We had a lot of problems with circlips coming out of the grooves on some of the highly modified Kawasaki Quads around 1986 or 1987. Kawasaki cured the problem by increasing the wire diameter of the circlip and machining the circlip grooves for the larger wire diameter.
Damn, thanks Neil and Jerry, sure enough, the one in the picture had not completely landed in the groove. I turned it a little so the gap would be towards the crank more and bam, fell right into place. Checked the gap and it was good. Thanks so much for noticing and saying something. It looked good to me when I first put it in, but I wasn't at the best angle. You probably just saved me from that failure. Definitely owe you both a beer!!!
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I always use a old wrist pin to push the circlip into the groove